1. Field
The invention is in the field of methods and apparatus for the production of oil and associated precious metals from mined oil-bearing rock material, especially the production of bitumen from tar sands and of kerogen products from oil shale.
2. State of the Art
In most instances, oil is produced from underground oil-bearing rock material by in situ methods which involve drilling thereinto, and by sometimes applying secondary or tertiary methods of recovering the oil from interstices of the underground formation. Oil-bearing rock material consists primarily of rock material having sedimentary organic matter in the form of petroleum or kerogen interspersed between the particles of rock which may be consolidated or unconsolidated.
Some oil-bearing deposits, commonly called tar sands, consist of oil-bearing rock material containing petroleum, wherein the petroleum is composed primarily of heavy hydrocarbons called bitumen, the lighter hydrocarbons having been mostly driven out at some previous time. (Tar sands is a misnomer since the organic matter is not tar and the rock may not be sand.) Bitumen has a very high viscosity, which is generally not compatible with in-situ production methods, and, thus, efforts to produce oil from tar sands by such methods are generally not economical (although, one promising method is that disclosed in Nielson, U.S. Pat. No. 4,856,587).
Bitumen is a very valuable binder product for hard-surfacing highways. Currently, it is state-of-the-art to utilize the residue from oil-cracking plants as a binder to mix with sand to produce a surfacing product. However, modern oil-cracking technology has progressed to the point that the residue is largely denuded of its binding characteristics. Standard tests have shown that the bitumen from some deposts, such as those of Asphalt Ridge, Utah, stretch 100 cm whereas the conventional binders stretch only 8 to 15 cm. This superior stretching characteristic of bitumen makes the road surface much more resistant to cracking under extreme temperature variations. Since it is reported that 60% of the highways in the U.S. need to be resurfaced and new highways are continually needed, the potential market for bitumen is obvious.
Another important consideration is that some deposits of tar sand, such as those of Asphalt Ridge, Utah, and P. R. Springs, Utah, are reported to contain commercial quantities of microscopic particles of precious metals such as gold, silver, platinum, palladium, and others. Consequently it would be highly desirable to have a production method for the bitumen which would also recover the precious metals.
For some deposits the tar sands are sufficiently close to the surface that they can be mined. For such deposits, the tar sands are mined and the bitumen subsequently produced by various methods.
One such method involves heating the tar sands in a retort operated at a temperature high enough to volatilize the bitumen. Typical of this method is the LURGI-RUHR GAS (L-R) process. In this process, hot spent sand is used as a fine-grained heat carrier to volatilize the bitumen. The spent sand is heated to 1200.degree. F. and mixed with fresh tar sand at a ratio of five parts hot spent sand to one part fresh tar sand. Most of the bitumen is volatilized in the mixing bin and must then be recovered by a condensation process. This method does not recover precious metals that may reside in the tar sands.
Another method is known as the "cold water" or "ambient temperature" flotation process. In this process, tar sand, water, and flotation reagents are fed into a semi-autogenous grinding (SAG) mill. Discharge from the SAG mill is split and ground to a required fineness in a rod mill. Slurry from the rod mill is then agitated and fed to a flotation plant having rougher-scavengers and a three-stage cleaning circuit which produces a bitumen concentrate. So far as is known, no provision is made for the recovery of precious metals.
Still another method is known as the "hot water" extraction process, which utilizes hot water rather than cold water. The resulting bitumen slurry is then mixed with a diluent and passed through a centrifuge to remove entrained matter and free water. The diluent is then removed by heating the mixture to about 600.degree. F. and distilling it, thus producing a bitumen concentrate. So far as is known, no provision is made for the recovery of precious metals.
Oil shale is a nomenclature commonly applied to oil-bearing rock containing organic matter in the form of kerogen. (Oil shale is a misnomer since the organic matter is not in the form of oil and the rock may not be shale.) Kerogen is a solid having a very complicated long-chain molecular structure, which may be converted to oil, various gases, and a solid residue by pyrolysis at temperatures usually exceeding 900.degree. F.
Pyrolysis is sometimes performed on in-situ deposits and sometimes on mined rock material. The normal procedure involves volatilizing the oil products resulting from pyrolysis and later fractionating and condensing them. One such process is the Aostra Taciuk process developed by William Taciuk of UMATAC Industrial Processes. However, this process volatilizes essentially all of the hydrocarbons, producing little, if any bitumen. This method is not amenable to the recovery of precious metals.
A very significant problem associated with the production of oil from mined oil-bearing rock material, whether tar sands or oil shale, is the disposition of the spent rock after the production of the oil. Typically, the spent rock still has a significant amount of residual oil remaining with it. The sheer volume of such rock constitutes an environmental problem of major proportions that must be carefully addressed when disposing of such rock.